Circuit breaker

ABSTRACT

A circuit breaker comprises a casing, a pair of contacts mounted on the casing, and a member movable between a position bridging said contacts for closing a circuit and a position opening said circuit. The bridging member is adapted to flex to a selected extent in response to a selected current in the circuit and a pair of upstanding arms on the bridging member are adapted to move apart to a selected extent in response to such flexing of the member. First biasing means mounted in the casing bias the bridging member to its open circuit position. A bushing having a central bore is then mounted on the casing, the bore having first and second diameter portions connected by a shoulder within the bore which faces the bridging member. An operating member is slidable in this bore between open and closed circuit positions thereof, the operating member having a recess at one end facing the bridging member and having at least one peripheral aperture opening into the recess. Second biasing means engage the operating member and the bushing for biasing the operating member to its open circuit position. A first latching member has a cam portion slidable in the operating member recess and has a shank portion extending from the recess. A second latching member is slidably mounted on this shank portion of the first latching member; a latching ball is disposed within the aperture opening into the operating member recess and engages the cam portion of the first latching member therein; and a third biasing means engaging the first and second latching members biases the cam portion of the first latching member away from the second latching member. The second latching member normally engages the arms of the bridging member for holding the bridging member in its closed circuit position and for biasing the cam portion of the first latching member to cam the latching ball through the operating member aperture into engagement with the shoulder in the bushing bore to releasably hold the operating member in its closed circuit position. However, the second latching member is adapted to be released from its engagement with the bridging member arms in response to said movement of the arms, thereby to release the cammed engagement of the latching ball with the shoulder within the bushing bore and to permit the operating member and the bridging member to move their open circuit positions in response to said biasing means. Manual force moving the operating member toward its open circuit position also serves to apply a force to the latching ball engaged by the bushing shoulder for camming the cam portion of the first latching member toward the second latching member against the bias of the third biasing means, thereby to permit the latching ball to disengage the bushing shoulder and to permit the operating member and the bridging member to move to their open circuit positions in response to the first and second biasing means.

United States Patent David E. Clarke Primary ExaminerDavid Smith, Jr. Attorneys-Harold Levine, Edward J. Connors, Jr., John A.

l-laug, James P. Mc Andrews and Gerald B. Epstein ABSTRACT: A circuit breaker comprises a casing, a pair of contacts mounted on the casing, and a member movable between a position bridging said contacts for closing a circuit and a position opening said circuit. The bridging member is adapted to flex to a selected extent in response to a selected current in the circuit and a pair of upstanding arms on the bridging member are adapted to move apart to a selected extent in response-to such flexing of the member. First biasing means mounted in the casing bias the bridging member to its open circuit position. A bushing having a central bore is then mounted on the casing, the bore having first and second diameter portions connected by a shoulder within the bore which faces the bridging member. An operating member is slidable in this bore between open and closed circuit positions thereof, the operating member having a recess at one end facing the bridging member and having at least one peripheral aperture opening into the recess. Second biasing means engage the operating member and the bushing for biasing the operating member to its open circuit position. A first latching member has a cam portion slidable in the operating member recess and has a shank portion extending from the recess. A second latching member is slidably mounted on this shank portion of the first latching member; a latching ball is disposed within the aperture opening into the operating member recess and engages the cam portion of the first latching member therein; and a third biasing means engaging the first and second latching members biases the cam portion of the first latching member away from the second latching member. The second latching member normally engages the arms of the bridging member for holding the bridging member in its closed circuit position and for biasing the cam portion of the first latching member to cam the latching ball through the operating member aperture into engagement with the shoulder in the bushing bore to releasably hold the operating member in its closed circuit position. However, the second latching member is adapted to be released from its engagement with the bridging member arms in response to said movement of the arms, thereby to release the cammed engagement of the latching ball with the shoulder within the bushing bore and to permit the operating member and the bridging member to move their open circuit positions in response to said biasing means. Manual force moving the operating member toward its open circuit position also serves to apply a force to the latching ball engaged by the bushing shoulder for camming the cam portion of the first latching member toward the second latching member against the bias of the third biasing means, thereby to permit the latching ball to disengage the bushing shoulder and to permit the operating member and the bridging member to move to their open circuit positions in response to the first and second biasing means.

PATENTED FEB] s |97| .SHEET 2 UF 4 Inventor, David E. Clark In ,a known circuit breaker construction, a thermally responsive contactbridging member is adapted to flex in response to an overload current in the breaker circuit, the member having apair of upstanding arms the ends of which are adapted to move apart as the member flexes. A latching mechanism engages the bridging member arms for holding the bridging member in a closed circuit position against a bias and is adapted to release its engagement with the bridging member arms as the arms move apart in response to an overload current, thereby to permit the bridging member to move to its open circuit position in response to said bias. The engagement of the latching mechanism with the bridging member arms is also utilized to move the thermally-responsive bridging .member between its open and closed circuit positions when operating the circuit breaker as a manually operable switch. This device operation by means of engagement between the latching mechanism and bridging member arms is found to be particularly advantageous in that the device can be repeatedly operated as a manual switch without tending to vary the thermal response characteristics of the bridging member. However, it has been found that the latching mechanism required for use in this device has been unduly complex and expensive and has been bulky and of inadequatereliability.

It is an object of this invention to provide a novel and improved thermally-responsive circuit breaker device; to provide such a device which is also adapted for repeated opera tion as a manual switch; to provide such a device which is operable as a switch without tending to vary its thermal response characteristics; and to provide such a device which incorporates a particularly inexpensive, compactand reliable latching mechanism.

Other objects, advantages and details of the circuit breaker of this invention appear in the following detailed description of preferred embodiments of the invention, the detailed description referring to the drawings in which:

. FIG. 1 is an elevation view, in section, of one embodiment of the circuit breaker of this invention; I FIG. 2 is a section view along line 2-2 of FIG. 1;

FIG. 3 is a section view along line 3-3 of FIG..l;

- FIG. .4 is an elevation view similar to FIG. 1 illustrating an alternate position of the circuit breaker shown in FIG. 1;

FIG. 5 is an elevation view similar to FIG. 2 illustrating an alternate position of the circuit breaker shown in FIG. 1;

FIG. 6 is an elevation view similar to FIG. 1 illustrating an alternate embodiment of the circuit breaker of this invention; and

FIG. 7 is an elevation view similarto FIG. 4 illustrating an alternate position of the circuit breakershown in FIG. 6.

Referring to the drawings, 10 in FIGS. l-5 indicates a preferred embodiment of the novel and improved circuit breaker of this invention. As shown, the circuit breaker includes a base or casing 12 comprising a pair of interfitting casing members 14 and 16 formed of a suitably rigid, electrically insulating material such as a moldable phenolic resin conventionally used in such casings. The casing members 14 and 16 are secured together by a plurality of threaded fasteners 18 as is best illustrated in F IGS. 1 and 3.

Each of the casing members 14 and 16 provides complementary shaped recesses 20 and 22 for respectively receiving electrically conductive metal terminals 24 and 26. The casing member recesses and the terminals 24 and 26 are cooperatively shaped as illustrated so that, when the terminals arepositioned between the casing members and when the casing members are secured togetherwith the threaded means 18, the terminals are fixed securely in place within the circuit breaker 10. As shown, the terminals 24 and 26 respectively mount electrical contacts 28 and 30 for holding said contacts in fixed position within the circuit breaker l0.

The circuit breaker 10 further includes a thermally responsive bridging contact member 32 such as is illustrated and described in US. Pat. No. 3,210,501 issued in the name of the present inventor to the assignee of the present invention on Oct. 5, 1965. That is, the bridging contact member 32 embodies a composite bimetallic member 34 formed of a layer of metal 36 of relatively high coefficient of thermal expansion,

and a layer of metal 38 of relatively low coefficient of thermal expansion, these metal layers being bonded together. The bridging member 32 further embodies a pair of electrically conductive U-shaped metal strips 40 and 42 each of which encloses one edge of the bimetallic member 34. U-shaped electrically insulating elements 44 and 46 are then disposed between the respective U-shaped metal strips and the bimetallic member 34 as shown in FIG. 1. A pair of electrical contacts 48 and 50 are then secured in electrically conductive relation to the respective U-shaped strips 40 and 42 by welding or the like. In addition, each of the U-shaped metal strips 40 and 42 is provided with a respective upstanding arm 52 and 54, which may be formed integral with the respective U-shaped metal strip. In a preferred embodiment of'the bridging contact member 32, the bimetallic member 34, only an edge of which is illustrated in FIG. 1, is substantially in sheet form but has a plurality of slots alternately extending into the bimetallic sheet from the left and from the right as the member 34 is viewed in FIG. 1. These slots give the bimetallic member the form of a continuous strip of bimetallic material made up of a plurality of interconnected elements each extending transversely between the U-shaped metal strips 40 and 42. One end of this continuous strip is electrically connected to the U-shaped metal strip 40 by welding or the like while the other end of the continuous strip is electrically connected to the U-shaped metal strip 42 in similar manner. The U shaped insulating strips 44 and 46, preferably formed of glass fibers embedded in a thermosetting plastic,-are then bonded to the respective U-shaped metal strips 40 and 42 and to the bimetallic member 34, thereby to electrically insulate the transverse elements of the bimetallic member from the U-shaped metal strips except at the ends of the continuous bimetallic strip formed by these transverse elements. In this construction, the electrical contact 48 is electrically connected m; contact 50 through the U-shaped metal strip 40, through the continuous strip of bimetallic material formed by the bimetallic member 34, and through the U-shaped metal strip 42, thereby to form an electrical circuit to bridge the fixed contacts 28 and 30 of the circuit breaker 10. In this arrangement, when sufficient electrical current is flowing through this circuit between the contacts 28 and 30, the bimetallic member 34 is adapted to be heated and to flex upwardly to the position indicated by the broken lines 56 in FIG. 1, this upward flexing being accompanied by lateral movement of the arms 52 and 54 to the positions indicated by the broken lines 58 and 60 respectively in FIG. 1. As the construction and function of the bridging contact member 32 is adequately described in the patent mentioned above, the member is not further described herein.

Referring further to FIG. 1, the thermally responsive bridging contact member 32 in the circuit breaker 10 is resiliently biased for linear movement from the position indicated in FIG. 1 to the position indicated in FIG. 4 by means of a compression spring 62. One end of this spring 62 abuts the closed end of a socket 64 formed by the casing members 14 and 16. An additional socket member 66 slidably mounted in strips 40 and 42 of the bridging contact member 32 for biasing the bridging contact member upwardly to open-contacts position as shown in FIG. 4. As will be be understood, the socket member 66 is formed of a suitably rigid electrically insulating material such as the molded phenolic resin material embodied in the casing members 14 and 16. Preferably the casing members 14 and 16 are provided with bosses 68 molded therein for engaging the bridging contact member 32 as shown in FIG. 4 for limiting movement of the member in response to the bias of the spring 62. As the construction and function of the biasing means including the spring 62 are adequately describedin the patent mentioned above, these biasing means are not further described herein.

In accordance with this invention, the circuit breaker is provided with a simple, compact, reliable and inexpensive latching mechanism generally indicated at 70 in FIGS. 1-5. As shown, this latching mechanism includes a bushing member 72 having a pair of flanges 74 and 76 thereon which are interfitted in complementary shaped recesses formed by the casing members 14 and 16 for securely mounting the bushing in a fixed position with respect to the casing member. Preferably, as illustrated in FIG. 3, the bushing flanges 74 and 76 are provided with flats 78 which, by reason of their interfitting in the complementary shaped recesses formed by the casing members, prevent rotation of the bushing with respect to the casing members. The bushing has a central bore 80 having a portion82 of a first diameter separated from a second portion 84 of a second diameter by a fir'st annular shoulder 86,

the second portion of the bore being adjacent to, a bore portion 88 of relatively larger diameter and being joined to the larger diameter portion, by a second shoulder 90. The bushing .72 is preferably threaded as indicated at 91 to facilitate mounting of the circuit breaker 10 on a control panel or the bore 80.- This operating memberhas a first portion 94 of a diameter corresponding to the'first bore portion 82 and a second portion 96 of a diameter small enough to fit through vthe bore 80 past the bore shoulder 86 as shown, these operating member portions being separated by a shoulder 95. The manual operating member is provided with a cylindrical recess 98 at one end thereof and two apertures 100 and 102 extending through the periphery of the operating member open into the recess 98.

In a preferred embodiment of this invention, the manual operating member 92 is formed of three elements 101, 103 and 105 which are'secured together to form the operating member by a threaded screw 106. This screw has a head 108 located in a recess'110 in the element 101 and has its opposite end extending through the element 103 and threadedly engaged with the element 105. In this-preferred construction, the upper element 101 of the operating member is preferably formed of a dark colored material while the intermediate element 103 is formed of a light colored material. While the elements 101. and 103 may be formed .of metal, these elements may also be formed of plastic materials to permit greater contrast between the colors of the elements. Preferably, a cover member 112, which may be marked with suitable indicia (not shown), is cemented or otherwise secured in the recess 110 to prevent tampering with the screw 106. Preferably, also, the operating member 92 is provided with a grippingportion 114 of relatively large diameter and with a shoulder 116 which limits the extent to which the operating member can be moved into the bore 80 of the bushing 72.'ln a preferred construction, the operating member 92 and the bushing 72 are provided with respective axial slots 118 and 120 and a detent 122 is forced into the bushing material to extend into the operating member slot, thereby to prevent rotation of the operating member within the bushing. See FIG. 3.

In accordance with this invention, a'helical coil compression spring 124 is disposed within the bushing bore 80 to engage the bushing bore shoulder 86 and the operating member shoulder 95 at opposite ends of the spring 124, thereby to bias the operating member upwardly as viewed in FIG. 1.

In accordance with this invention, the latching mechanism 70 further includes a first latching member 126 of generally cylindrical configuration. This latching member has a central,

. first latching member are proportioned to fit slidably within the recess 98 in the manual-operating member 92 as shown in FIG. 1. The firstlatching member126 further includes a shank portion 138 joined to the larger diameter portion 132 by a shoulder 140, the shank portion extending out of the operating member recess 98 and having a retaining-ring I42 provided at the distal end thereof.

In accordance with this invention, the latching mechanism 70 also includes a second latching member 144 which comprises a washerlike member of rigid, electrically insulating material or the like. This second latching member has a centr'al bore 146, counterbored at 148 and 150, which is fitted over the shank portion 138 of the first latching member and which is retained on said shank portion by the retaining ring 142. A helical coil compression spring 152 fitted over the shank portion of the first latching member is then engaged with the second latching member within the counterbore 148 and with the shoulder 140 on the first latching member, thereby to bias the second latching member away from the conical portions of the first latching member. The second latching member 144.is also provided with a downwardly facing shoulder 154. For example, in a preferred construction,

the shoulder 154 is formed by embedding a metal ring 156 in the molded phenolic resin or other. electrical insulating material embodied in the second latching member.

In accordance with this invention, two latching balls 158 are disposed in the apertures and 102 in the operating member, these balls being formed of steel or other suitably rigid material and being proportioned to extend out of the operating member apertures 100 1 and 102 at both sides thereof.

The operation of the circuit breaker 10 will now be discussed. In this regard, FIGS. 1 and 2' illustrate the circuit breaker 10 in its closed contacts position in which an electrical circuit is formed between the breaker terminals 24 and 26. That is, as shown in FIGS. 1 and 2, the bridging contact member 32 has its contacts 48 and 50 engaged with the fixed contacts 28 and 30, thereby to electrically connect the terminals 24 and 26 through the U-shaped metal strips 40 and 42 and through the bimetallic member '34. Although the bridging contact member 32 is biased by the spring 62 to move to the open contacts position shown in FIGS. 4 and 5, the engagement of the arms 52 and 54 of the bridging contact member with the shoulder 154 in the latching mechanism 70 retains the bridging contact member in closed contacts position as shown in FIGS. 1 and 2. That is, when the manual-operating memberis in the depressed position shown in FIGS] and 2, the latching balls disposed in the operating member apertures 100' and 102 are engaged with the shoulder 90 within the bushing 72, thereby retaining the operating member in the position shown against the bias ofthe spring 124. On the other hand, the latching balls 158 are retained in engagement with the bushing shoulder 90 by theengag'ement between the balls and the conical cam surface 136 of the first latching member 126. The first latching member, in turn, is held'in engagement with the latching balls by action of the spring 152 which, in the arrangement shown in FIGS. 1 and 2 is compressed between the shoulder on the first latching member and the second latching member 144. That is, the engagement of the shoulder 154 of the second latching member with the arms 52 and 54 of described circuit between the breaker terminals 24 and 26,

the bimetallic member 34 of the bridging contact member 32 becomes heated and flexes upwardly to the position shown by,

latching member 144 first moves downwardly in response to the bias of the spring 152 to engage the retaining ring 142. At this point, the spring 152 is in its position of repose. The first and second latching members then move downwardly together to release the engagement between the latching balls 158 and the conical surface 136 of the first latching member. As the engagement of the conical surface 136 is released, the latching balls 158 move further into operating member recess 98 releasing their engagement with the bushing shoulder 90, thereby permitting the operating member, together with the latching balls and with the first and second latching members,

to move to the position shown in FIGS. 4 and 5 in response to the bias of the spring 124. Also, as soon as the arms 52 and 54 of the bridging contact member are released from their engagement with the shoulder 154 in the latching mechanism 70, the bridging contact member 32 is moved to the open contacts position illustrated in FIGS. 4 and 5 in response to the bias of the spring 62. As illustrated in FIGS. 4 and 5, upward movement of the operating member 92 in response to the spring 124 is limited by engagement of the latching balls between the first latching member 126 and the shoulder 86 on the bushing 72. Upward movement of the bridging contact member in response to the spring 62 is limited by the engagement of the bridging contact member with the bosses 68 in the circuit breaker casing. In the position,.shown in FIGS. 4 and 5, the light-colored element 103 of the operating member 92 is exposed to view outside the bushing 72 giving visual indication that the circuit breaker is in open circuit position.

If the circuit breaker is, in closed circuit position as shown in FIGS.] and 2 and-rnanual opening of the breaker circuit is desired, the. manual operating member 92 need only be pulledwith selected force. This pulling on the operating member exerts a corresponding upward force on the latching balls so that the balls are cammed inwardly by the bushing shoulder 90, this inward movement of the balls'camming the first latching member downwardly against the bias of the spring 152. As soon as the latching balls are cammed inwardly to a sufficient extent to clear the bushing shoulder 90, the operating member, together with-the balls and with the first and second latching members, moves rapidly to open contacts position under the bias of the spring 124'. This movement is accompanied by upward movement of the bridging contact member 32 in response to the bias of the spring 62 for rapidly opening the breaker circuit.

When the circuit breaker is in the open contacts position shown in FIGS. 4 and 5, the circuit breaker is returned to closed contacts position by merely depressing the manualoperating member 92 against the bias of the spring 124.

Downward movement of the operating member also moves the latching balls and the first and second latching members in the same direction. The shoulder 154 of the second latching member then normally engages the arms 52 and 54 of the bridging contact member 32 for moving the bridging contact member downwardly to closed circuit position against the bias of the spring 62. As the contacts 48 and 50 initially engage the fixed contacts 28 and 30while depression of the operating 7 member is continued, the spring 152 is compressed and moves the first latching member upwardly to cam the latching balls 158 out of the operating member recess 98 into latching engagement with the bushing shoulder 90. However, if manual closing of the circuit breaker is attempted too quickly after the circuit breaker has opened in response to an overload current as above described such that the bimetallic member in the the circuit breaker 10 which correspond to similar com ponents of the circuit breaker 10 are identified by corresponding primed numbers in FIGS. 6 and 7 and are not further described herein. In this alternate embodiment of the circuit breaker of this invention, an even more compact version of the latching mechanism 70 is achieved by use of an alternate bushing construction as indicated at in FIGS. 6 and 7. That is, the bushing 160 has a central bore 162 which includes a first portion 164 of relatively small diameter and a second portion 166 of relatively larger diameter, these two bore portions being connected by a shoulder 90. A metal bushing ring 168 having a central aperture 170 and a flange 172 is then press-fitted or otherwise secured over an end of the bushing 160 within the casing of the circuit breaker 10. In this construction, the manual-operating member 92' is provided with a first relatively large diameter portion 174 slidably fitted within the first diameter portion 164 of the bushing bore 162. The manual-operating member is also provided with a second relatively smaller diameter portion 176 joined to the first diameter portion 174 by a shoulder 178. The manual-operating member is further provided with a cylindrical recess 98' and with apertures 100 and 102 as in the circuit breaker 10 previously described. However, in the circuit breaker 10', the apertures 100 and 102' are formed in the larger diameter portion of the operating member at a location above the operating member shoulder 178.

In accordance with this invention, a helical coil compression spring is disposed around the smaller diameter portion of the operating member to engage the shoulder 178 and the ring 168 on the bushing 160, thereby to bias the operating member 92' upwardly as viewed in FIG.

In this arrangement, when the circuit breaker 10' is in closed contacts position as illustrated in FIG. 6, the manualoperating member 92 is retained in the depressed position shown against the bias of the spring 180 by engagement of the latching balls 158' with the bushing shoulder 90'. The latching balls 158 are held in this latching engagement with the shoulder 90 by engagement between the balls and the conical surface 136' of the first latching member 126. The first latching member 126', in turn, is held in its position by engagement of the shoulder 154' in the second latching member with the arms 52' and 54' of the bridging contact member 32 and by compression of the spring 152' between the first and second latching members.

When the circuit breaker 10' is subjected to and an overload current between the breaker terrninals 24 and 26' so that the second latching member 144 is released from its engagement with the bridging contact arms 52' and 54', the second latching member moves downwardly under the bias of the spring 152' until the spring reaches its position of repose thereby releasing the spring force on the first latching member. The upward bias of the spring 180 then cams the latching balls 158' inwardly so that the balls, now released from any latching force exerted by the first latching member, are released from their latching engagement with the bushing shoulder 90. The operating member 92', the balls and the first and second latching members then move upwardly in response to the spring 180 while the bridging contact member 32' moves to its open contacts position in response to the bias of the spring 62 as shown in FIG. 7. The circuit breaker 10 can also be manually opened by pulling on the operating member 92 and can be manually closed by depressing the operating member in the manner above described as will be understood.

It should be understood that although preferred embodiments of the circuit breaker of this invention have been described by way of illustration, this invention includes all modifications and equivalents thereof falling within the scope of the appended claims.

Iclaim:

l. A latching mechanism for releasably restraining linear movement of a selected membertfrom a first position to a second position, said mechanism comprising a bushing having a central bore fixedly mounted with respect to said member,

and-said bushing bore having first and second diameter portions connected by a shoulder which faces said member, an operating member slidable in said'bore between first and .secbnd positions thereof, said operating member having a recess in one end facing said selected member and having a peripheral aperture opening into said recess, means engaging said bushing and operating member biasing said operating member to saidfirst position thereof, a first latching member having a cam portion slidable in said recess and having a shank portion extending from said recess, a" latching ball in said operating memberaperture engaging said cam portion of said first latching member, a second latching member slidably tion, said operating member being manually movable toward said second operating member position for camming said latching ball against said bushing shoulder to cam said cam portion of said first latching member toward said second latching member against said additional biasing means to release saidlatching engagement of said ball and bushing shoulder, thereby to permit said operating member, ball and first and second latching members to move to said second operating member position for. releasing said selected member for movement to said second position thereof.

2. A circuit breaker comprising acasing, a pair of contacts mounted on said casing, a member movable between a position bridging said contacts for closing a circuit and a position opening said circuit, said bridging member flexing to a selected extent in response to selected current in said circuit and having a pair of spaced arms which curve apart to a selected extent in response to said flexing of said member, first biasing means mountedon said casing biasing said bridging member to said open circuit position, a bushing having a central bore mounted on said casing, said bore having first and second diameter portions connected by a shoulder which faces said bridging member, an operating member slidable in said bore between open and closed circuit positions, said operating member having a recess in one end facing said bridging member and having a peripheral aperture opening into said recess, second biasing means engaging said operating member and said bushing biasing said operating member to said open circuit position, a first latching member having a cam portion slidable in said recess and having a shank portion extending from said recess, a latching ball in said operating member aperture in engagement with said cam portion of said first latching member, a second latching member slidably mounted on said shank portion of said first latching member, and third biasing means engaging said first and second latching members biasing said cam portion of said first latching member away from said second latching member, said second latching member normally engaging said bridging member arms for holding said bridging member in said closed circuit position thereof and for biasing said first latching member to cam said latching ball into engagement with said bushing shoulder to releasably hold said operating member in said closed circuit position thereof, said second latching member being releasable from engagement with said bridging member arms in response to said arm movement for releasing cammed engagement of said ball with said bushing shoulderand for permitting said operating member and bridging member to move to said open circuit positions.

3. A circuit breaker as set forth in claim 2 wherein said bushing bore has a third diameter portion connected to said first and second bore portions by a second bushing shoulder and wherein said operating member has a first diameter portion slidably engaged with said third bushing bore portion and has a second diameter portion connected to said first operating member portion by an operating member shoulder, said second biasing means comprising a helical compression spring disposed around said second diameter portion of said operating member in engagement with said operating member shoulder and with said second bushing shoulder for biasing said operating member to said open circuit position thereof.

4. A circuit breaker as set forth in claim 2 wherein a ring is 

1. A latching mechanism for releasably restraining linear movement of a selected member from a first position to a second position, said mechanism comprising a bushing having a central bore fixedly mounted with respect to said member, and said bushing bore having first and second diameter portions connected by a shoulder which faces said member, an operating member slidable in said bore between first and second positions thereof, said operating member having a recess in one end facing said selected member and having a peripheral aperture opening into said recess, means engaging said bushing and operating member biasing said operating member to said first position thereof, a first latching member having a cam portion slidable in said recess and having a shank portion extending from said recess, a latching ball in said operating member aperture engaging said cam portion of said first latching member, a second latching member slidably mounted on said shank portion of said first latching member, and additional biasing means engaging said first and second latching members biasing said cam portion of said first latching member away from said second latching member, said second latching member manually engaging said selected member for restraining said selected member in said first position thereof and for biasing said cam portion of said first latching member to cam said latching ball into latching engagement with said bushing shoulder for releasably holding said operating member in said first operating member position, said operating member being manually movable toward said second operating member position for camming said latching ball against said bushing shoulder to cam said cam portion of said first latching member toward said second latching member against said additional biasing means to release said latching engagement of said ball and bushing shoulder, thereby to permit said operating member, ball and first and second latching members to move to said second operating member position for releasing said selected member for movement to said second position thereof.
 2. A circuit breaker comprising a casing, a pair of contacts mounted on said casing, a member movable between a position bridging said contacts for closing a circuit and a position opening said circuit, said bridging member flexing to a selected extent in response to selected current in said circuit and having a pair of spaced arms which curve apart to a selected extent in response to said flexing of said member, first biasing means mounted on said casing biasing said bridging member to said open circuit position, a bushing having a central bore mounted on said casing, said bore having first and second diameter portions connected by a shoulder which faces said bridging member, an operating member slidable in said bore between open and closed circuit positions, said operating member having a recess in one end facing said bridging member and having a peripheral aperture opening into said recess, second biasing means engaging said operating member and said bushing biasing said operating member to said open circuit position, a first latching member having a cam portion slidable in said recess and having a shank portion extending from said recess, a latching ball in said operating member aperture in engagement with said cam portion of said first latching member, a second latching member slidably mounted on said shank portion of said first latching member, and third biasing means engaging said first and second latching members biasing said cam portion of said first latching member away from said second latching member, said second latching member normally engaging said bridging member arms for holding said bridging member in said closed circuit position thereof and for biasing said first latching member to cam said latching ball into engagement with said bushing shoulder to releasably hold said operating member in said closed circuit position thereof, said second latching member being releasable from engagement with said bridging member arms in response to said arm movement for releasing cammed engagement of said ball with said bushing shoulder and for permitting said operating member and bridging member to move to said open circuit positions.
 3. A circuit breaker as set forth in claim 2 wherein said bushing bore has a third diameter portion connected to said first and second bore portions by a second bushing shoulder and wherein said operating member has a first diameter portion slidably engaged with said third bushing bore portion and has a second diameter portion connected to said first operating member portion by an operating member shoulder, said second biasing means comprising a helical compression spring disposed around said second diameter portion of said operating member in engagement with said operating member shoulder and with said second bushing shoulder for biasing said operating member to said open circuit position thereof.
 4. A circuit breaker as set forth in claim 2 wherein a ring is attached to said bushing to extend partly over said bushing bore and wherein said operating member has a first diameter portion slidably engaged with said first bushing bore portion and has a second diameter portion connected to said first operating member portion by an operating member shoulder, said second biasing means comprising a helical compression spring disposed around said second operating member portion in engagement with said bushing ring and with said operating member shoulder for biasing said operating member to said open circuit position thereof. 